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When asked about their driving skills, 84% of college students rated themselves above average. Clearly, this is unlikely to be the case. In investing, the overconfidence bias manifests itself through excess trading, as the investor believes his ideas more accurate and better interpreted than everyone else’s.

In a study of discount brokerage trading, men were found to trade more than women, and the excess trading did not result in higher returns. In fact, the commissions resulted in lower net returns. This study supports a thesis that men are overconfident investors. Furthermore, the overconfidence results in selecting riskier stocks on average.